Organic peroxides are widely used in the polymer industry to modify various resins such as through grafting reactions, cross-linking reactions, and modification of melt flow, for example. However, by their very nature, peroxides are heat sensitive, degrade quickly and can be dangerous if improperly handled in a concentrated form.
To increase safety and ease of handling, peroxides are often sold as diluted solutions in solvents such as in odorless mineral spirits, or as blends with solid inorganic fillers, such as diatomaceous earth, silica, clays, or calcium carbonate. While these peroxide formulations have their uses, the solvent or filler functions merely to dilute the peroxide. Thus, the solvent and fillers do not enhance the properties of the polymer to be modified by the peroxide formulation.
Another technique for increasing the safety and ease of handling peroxides has been the development of peroxide masterbatches. A masterbatch is a composition in which a compound, such as an organic peroxide, is blended with a carrier, typically a polymer, where the masterbatch polymer is compatible with the polymer or resin to which the masterbatch ultimately will be added (the latter polymer or resin being referred to hereinafter as a "host polymer or resin"). The peroxide or other component added to the carrier in the masterbatch should not react with the carrier so that the peroxide or other component is available for use when the masterbatch is mixed subsequently with the host polymer or resin.
The peroxide or other compound added to the carrier in the masterbatch is present in a concentration considerably higher than the concentration of the compound in the host polymer or resin into which the masterbatch is mixed. The advantages of peroxide masterbatches are that they can be prepared fairly readily, the peroxide is in a fairly stable form, and they are relatively safe and easy to store, ship and handle, particularly since masterbatches typically are formed into pellets or powders for ease of blending with the host polymer or resin to be treated. Furthermore, the masterbatches are formulated by using a polymer in the masterbatch which is identical to or very compatible with the host polymer or resin to be treated to assure good blending and compatibility.
European Patent Application Publication No. 0 227 048 A2, published Jul. 1, 1987, of Albee, Jr., discloses a peroxide masterbatch composition referred to as a peroxide catalyst concentrate. The concentrate is formed by homogeneously blending the peroxide in a polymer composition including at least two thermoplastic or wax polymers in which the combined polymer composition has a melt index of about 250 to about 2500 grams per 10 minutes at 190.degree. C., with an average softening point of about 50.degree. to 115.degree. C., and further in which the melting point range must be broad having at least two melting temperatures at which a substantial portion of the polymer composition melts at each temperature. Polycaprolactone is not one of the polymers mentioned as being suitable for inclusion in the peroxide concentrate composition.
U.S. Pat. No. 3,242,159 of Kaufman discloses a peroxide dispersed into linear polyethylene to form a masterbatch, which in turn is added to more linear polyethylene. The final linear polyethylene is heated to produce a cross-linked polymer. Fillers and additives, except antioxidants, are to be avoided in the cross-linking mixture.
U.S. Pat. No. 3,523,920 of Schultz discloses cross-linked polylactone homopolymers and methods for their preparation. An object of the invention disclosed in this patent is to provide new and useful cross-linked polylactones of improved thermal properties and outstanding solvent resistance. No mention is made whatsoever of any type of masterbatch composition of any sort. The cross-linked polylactones, which may include polycaprolactone, are produced by reacting the polylactones with a free radical forming system to effect cross-linking. Preferred free radical generators include organic peroxides, such as dicumyl peroxide, benzoyl peroxide, acetyl peroxide, 2,4-dichlorobenzoyl peroxide, stearoyl peroxide, di-t-butyl peroxide and t-butyl perbenzoate. Additional fillers can also be added, such as calcium carbonate, metal oxides, silica, neutral or basic carbon blacks, etc.
The cross-linked polylactones of Schultz U.S. Pat. No. 3,523,920 may be cross-linked by using about 0.5% to about 10% by weight of a peroxide (or other free radical initiator) based on the weight of polylactone. The peroxides may be added to the polylactone in a steam-heated rubber mill to mix and compound the peroxide with the polylactone to make an intermediate composition. The intermediate composition is then heated to effect cross-linking, typically after the composition is formed into sheets or other desired shapes.
The present invention, in contrast to Schultz, is not intended to produce cross-linked polycaprolactone, but rather, a masterbatch in which the polycaprolactone is the carrier in the masterbatch composition also including at least one organic peroxide, such that the organic peroxide can be used in subsequent reactions when the masterbatch composition is added to a host polymer or resin. In the present invention, the peroxide of the masterbatch composition does not substantially decompose to initiate the formation of free radicals until the masterbatch is added to or mixed with a host polymer or resin and free radical initiation is commenced intentionally by heating, radiation or other means well known to one skilled in the art. Moreover, the intermediate composition used to make the cross-linked polylactone composition of Schultz U.S. Pat. No. 3,523,920 contains about 0.5% to about 10% of an organic peroxide. However, the present invention contains greater than about of at least one organic peroxide. Thus, the present invention is directed to a composition outside of the range of any of the compositions disclosed in Schultz U.S. Pat. No. 3,523,920. The present invention has a completely different use, namely, as a masterbatch composition in which the peroxide can be safely and stably handled, transported and stored and still be available for subsequent use.
U.S. Pat. No. 3,594,342 of Ratzsch et al. discloses peroxide masterbatches using as carriers copolymers of ethylene and vinyl acetate or ethylene and acrylic esters, with a mean molecular weight of 1200 to 8000. Additives such as dyes, lamp-black and stabilizers may also be included.
U.S. Pat. No. 3,923,947 of Cook discloses a continuous process for preparing cross-linkable polyethylene in an extruder in which a peroxide compound with a flash point of at least 70.degree. C. is dispersed or dissolved in a liquid wax or oil compatible with the polyethylene composition. The dispersion or solution of peroxide is injected into molten polyethylene in a mixing zone at the nose end of the extruder. The hold-up time in the mixing zone is controlled to disperse the peroxide compound in the polyethylene melt uniformly and safely without substantial crosslinking.
U.S. Pat. No. 4,006,283 of MacKenzie, Jr. et al. discloses a method of applying liquid di-t-butyl peroxide to a polyolefin by introducing the peroxide in a vessel below a mass of particulate polyolefin. The polyolefin particles may be added in a batch to the vessel and initially treated with the peroxide. This is followed by the prompt addition of another or remaining batch of polyolefin particles and additional curing agent.
U.S. Pat. No. 4,342,844 of Torenbeek et al. describes coating polymer particles, such as polyethylene, with a liquid peroxide medium. The liquid medium comprises about 2-100% of a peroxide which is a liquid at about 15.degree.-95.degree. C. and 0-98% of a liquid in which the peroxide and the polymer are insoluble. A polymer masterbatch in which essentially all of the polymer particles are completely surrounded by the peroxide liquid medium is obtained.
U.S. Pat. No. 4,366,270 of Ruter discloses a process for incorporating additives into thermoplastic synthetic resins by forming a masterbatch including the additives carried in a polymerizable cyclic ester, which may be unpolymerized or polymerized before being added to the synthetic resin. The polymerizable cyclic ester may be caprolactone, such that when polymerized, the carrier may be polycaprolactone. The types of additives to be contained in the masterbatch are generally referred to as "customary additives for synthetic resins." There is no disclosure of the use of any organic peroxide as a component of the masterbatch composition. Rather than being customary additives which are retained in synthetic resins, organic peroxides are free radical initiators which are typically dissipated, decomposed or consumed in synthetic resins.
U.S. Pat. No. 4,397,992 of Johansson et al. discloses a peroxide masterbatch in which the carrier is a multistage graft copolymer comprising 70-90% of a hard portion made by graft polymerizing a monomer or monomers of lower alkyl methacrylates, styrene and mixtures thereof and a cross-linking agent onto 10-30% of a rubbery portion made by polymerizing a butadiene and/or lower alkyl crylate or a mixture of styrene and butadiene or acrylonitrile and butadiene. Optional reinforcing agents or fillers may be included.
U.S. Pat. No. 4,451,589 of Morman et al. discloses a peroxide masterbatch wherein an organic peroxide is mixed at high temperatures in extruders with carrier polymers and copolymers of propylene and butylene. More than half of the polymer and more than 0.01% of the peroxide remains unreacted after the masterbatch is initially pelletized.
A masterbatch of peroxide dispersed onto a filler is described in a Material Safety Data Sheet covering LUPERCO.TM. 101-P20 which is produced by the Organic Peroxides Division of Atochem North America, Inc. (formerly the Lucidol Division of the Pennwalt Corp.). Basically, this masterbatch consists of 2,5-dimethyl-2,5-di-(t-butylperoxy)hexane, silica, and polypropylene powder.
A masterbatch of peroxide dispersed onto a polymer is also described in a Material Safety Data Sheet covering LUPERCO.TM. 101-A5, also produced by the Organic Peroxides Divison of Atochem North America, Inc. (formerly the Lucidol Division of the Pennwalt Corp.). This masterbatch consists of 5% 2,5-dimethyl-2,5-di-(t-butylperoxy)hexane on acetal resin (formaldehyde homopolymer).
Nowhere in the prior art is the use of polycaprolactone as a carrier for organic peroxides mentioned or suggested. Nor is it mentioned that the carrier polymer itself of a peroxide-containing masterbatch can be used to improve upon the properties of the host resin to which the masterbatch is to be added.